This ''Applications'' article focuses on superquenching of the fluorescence of conjugated polyelectrolytes and related fluorescent polyelectrolytes and its applications to biosensing. Superquenching can occur for both aqueous solutions of these polymers as well as for various supported formats. For biosensing the supported formats are generally most practical. Three practical sensing applications are reviewed: nucleic acids, protease enzyme activity assays and kinase/phosphatase assays based on metal-ion-mediated superquenching.

No abstract

An assay for a target single strand 20-base sequence of DNA coding for the anthrax lethal factor, based on conjugated polymer fluorescence superquenching, is reported. The assay employs a platform in which the receptor (a biotinylated complementary sequence "capture strand") and polymer (two components: an anionic poly(phenylene ethynylene) (PPE) and a biotinylated -PPE) are co-located on streptavidinderivatized polystyrene microspheres. A conjugate of the target strand with the energy transfer quencher QSY-7 (DNA-QTL) is used to construct competition assays for the target. A direct competition assay between the target-DNA and DNA-QTL for the microsphere-bound capture is only marginally successful due evidently to greater kinetic affinity of the polymer-capture ensemble for the conjugate. However a sequential addition of target, followed by DNA-QTL affords a quantitative assay for the target by attenuation of PPE fluorescence quenching by the DNA-QTL. Likewise a direct competition in solution between the target and DNA-QTL for the biotinylated capture strand followed by addition of microspheres provides a sensitive and quantitative assay for the target single strand DNA.

A comprehensive study of a series of four monodisperse, metal-organic pi-conjugated oligomers of varying length is reported. The oligomers are based on the aryleneethynylene architecture, and they contain a 2,2'-bipyridine-5,5'-diyl (bpy) metal binding unit. The photophysical properties of the free oligomers and their complexes with the (L)Re(I)(CO)(3)X chromophore (where L = the bpy-oligomer and X = Cl or NCCH(3)) were explored by a variety of methods including electrochemistry, UV-visible absorption, variable temperature photoluminescence (PL), transient absorption (TA), and time-resolved electron paramagnetic spectroscopy (TREPR). The absorption of the free oligomers and the metal complexes is dominated by the pi,pi* transitions of the pi-conjugated oligomers. The free oligomers feature a strong blue fluorescence that is quenched entirely in the (L)Re(I)(CO)(3)X complexes. The metal-oligomers feature a weak, relatively long-lived red photoluminescence that is assigned to emission from both the (3)pi,pi* manifold of the pi-conjugated system and the dpi Re --> pi* bpy-oligomer metal-to-ligand charge transfer ((3)MLCT) state. On the basis of a detailed analysis of the PL, TA, and TREPR results an excited-state model is developed which indicates that the oligomer-based (3)pi,pi* state and the (3)MLCT states are in close energetic proximity. Consequently the photophysical properties reflect a composite of the properties of the two excited-state manifolds.